Voltage converter control circuits and methods

ABSTRACT

Voltage converter control circuits and methods. In some embodiments, a voltage converter can include a voltage conversion circuit having an inductor configured to be charged and discharged to facilitate conversion of an input voltage to an output voltage. The voltage conversion circuit can further include a switch configured to allow the inductor to be charged and discharged. The voltage converter can further include a logic drive unit configured to provide a drive signal to the switch to control the charging and discharging of the inductor. The voltage converter can further include a mode control unit configured to provide a mode-switching signal to the logic drive unit to control switching between a continuous control mode and a discontinuous control mode based on an inductance current associated with the inductor and a constant load-current threshold.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. Application Ser No.14/291,403 filed May 30, 2014, entitled MODE CONTROL DEVICE, VOLTAGECONVERTER, AND CONTROL METHOD USED IN THE VOLTAGE CONVERTER, the benefitof the filing date of which is hereby claimed and the disclosure ofwhich is hereby expressly incorporated by reference herein in itsentirety.

TECHNICAL FIELD

The present application relates to a field of electronic technique, andmore particularly, to a mode control device for a voltage converter, avoltage converter, and a control method used in the voltage converter.

BACKGROUND

Electronic apparatus typically includes therein electronic modules suchas different subsystems, electronic circuits, and so on. These modulesusually require different supply voltages for achieving normaloperations thereof. For example, an analog power amplifier may require asupply voltage of 3.5 volts, a digital processing module may requiredifferent supply voltages of 1.8 volts, 5 volts etc. To ensure normaloperations of the respective electronic modules in the electronicapparatus, a voltage converter is required to convert a DC voltage(e.g., a voltage from a battery) into another different DC voltage asrequired by an individual module, that is, a specific input voltage Vinis converted into a different output voltage Vout.

In existing voltage converters, for example, electric energy at an inputis stored transitorily in an inductor and/or a capacitor (i.e., acharging process is performed), and thereafter electric energy isreleased at a different voltage at an output (i.e., a dischargingprocess is performed), so that the input voltage Vin is converted intothe desired output voltage Vout. Accordingly, a drive signal is employedto drive a control device (e.g., a switch) in the voltage converter, bywhich the charging process and the discharging process are controlled soas to obtain the desired output voltage Vout, that is, a turn-on timeTon during which a corresponding switch is closed to charge and aturn-off time Toff during which the switch is open to discharge arecontrolled. The turn-on time Ton corresponds to a pulse width of thedrive signal.

In the operation process of the voltage converter, a situation whereimpedance of a load (e.g., an electronic module) driven by its outputvoltage Vout changes may occur, for example, when an operation state ofthe electronic module changes, and its impedance value relative to thevoltage converter will change. In this case, in order to improveconversion efficiency of the voltage converter, it may need to adoptdifferent control methods to control the charging operation anddischarging operation of the voltage converter. For example, when theload driven by the output voltage Vout is a medium or heavy load whoseload value is relatively large, a continuous control mode (CCM) may beadopted to control the voltage converter; when the load driven by theoutput voltage Vout is a light load whose load value is relativelysmall, a discontinuous control mode (DCM) may be adopted to control thevoltage converter. In the continuous control mode, the drive signaldrives a control device in the voltage converter to make the voltageconverter perform charging and discharging operations continuously; andin the discontinuous control mode, the drive signal drives a controldevice in the voltage converter, so that the voltage converter can haltfor some time after performing charging and discharging operations, andthereafter again perform charging and discharging operations.

When the load driven by the output voltage Vout changes from a mediumload into a light load, the control mode of the voltage converter needsto be switched from a continuous control mode to a discontinuous controlmode. Typically, mode switching is carried out based on load current onthe driven load, and threshold of the load current for carrying out modeswitching usually varies along with the input voltage Vin and the outputvoltage Vout of the voltage converter, which makes it difficult toperform mode switching accurately, thus lowers power efficiency of thevoltage converter accordingly. Further, variation of the on-offfrequency of the control device will also increase noise in the outputvoltage Vout.

SUMMARY

Aspects of the present application may relate to a mode control devicefor a voltage converter, a voltage converter, an electronic apparatusincluding the voltage converter, and a control method used in thevoltage converter etc.

The mode control device in an embodiment of the present application maybe applicable to controlling a voltage converter to switch from acontinuous operation mode to a discontinuous operation mode. The voltageconverter converts an input voltage to an output voltage Vout, which maybe used for powering a load. The voltage converter may comprise: avoltage conversion circuit including a control device and an inductor,the inductor being capable of performing charging and dischargingoperations, the control device for operating under driving of a drivesignal to control charging and discharging operations of the inductor; alogic drive unit for adjusting an operation mode for the voltageconversion circuit, and generating the drive signal for driving thecontrol device, so as to obtain a desired output voltage; and a modecontrol device for generating a mode switching signal that controlsswitching from a continuous control mode to a discontinuous control modebased on inductance current on the inductor, the mode switching signalenabling the voltage converter to be capable of switching from thecontinuous control mode to the discontinuous control mode at a constantload current threshold, in which case the load current threshold can beindependent of the input voltage and the output voltage of the voltageconverter.

The mode control device may include: an inductance signal detection unitfor detecting inductance current flowing on an inductor in the voltageconversion circuit, and outputting a detection signal; a compensationunit for compensating for change of an input voltage and an outputvoltage of the voltage converter so as to switch from a continuouscontrol mode to a discontinuous control mode at a constant load currentthreshold, and outputting a compensated switching thresholdcorresponding to the inductance current; and a mode switchingdetermination unit for determining whether to switch from the continuouscontrol mode to the discontinuous control mode based on the detectionsignal from the inductance signal detection unit and the switchingthreshold from the compensation unit, and generating a mode controlsignal indicating whether to switch from the continuous control mode tothe discontinuous control mode.

The mode control method according to an embodiment of the presentapplication may include: detecting inductance current flowing on aninductor for performing charging and discharging operations in a voltageconverter, and outputting a detection signal; compensating for change ofan input voltage and an output voltage of the voltage converter so as toswitch from a continuous control mode to a discontinuous control mode ata constant load current threshold, and outputting a compensatedswitching threshold corresponding to the inductance current; anddetermining whether to switch from the continuous control mode to thediscontinuous control mode based on the detection signal and theswitching threshold, and generating a mode control signal indicatingwhether to switch from the continuous control mode to the discontinuouscontrol mode.

In the technical solutions according to the embodiments of the presentapplication, whether to switch from a continuous control mode to adiscontinuous control mode is determined based on the inductance currentflowing on the inductor in the voltage converter, and change of theinput voltage and the output voltage of the voltage converter arecompensated when determining the switching threshold, so that thevoltage converter can switch from the continuous control mode to thediscontinuous control mode accurately at a constant load currentthreshold, which improves power efficiency of the voltage converter andreduces noise in the output voltage caused by change of the on-offfrequency in a control device.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly explain the technical solutions, drawingsreferenced in the description of embodiments or conventionaltechnologies are briefly introduced below. The drawings described beloware merely some embodiments of the present invention, a person ofordinary skill in the art can also obtain other drawings according tothese drawings. Identical reference numerals typically indicateidentical components throughout these drawings.

FIG. 1 is a block diagram schematically illustrating a voltage converterincluding a mode control device according to an embodiment of thepresent application;

FIG. 2 schematically illustrates a circuit diagram of a boost conversioncircuit in a boost converter;

FIG. 3 is a block diagram schematically illustrating the mode controldevice according to an embodiment of the present application;

FIG. 4 schematically illustrates a signal diagram of inductance currentof a buck converter in a PWM mode;

FIG. 5 is a circuit diagram schematically illustrating the compensationunit in FIG. 3;

FIG. 6 schematically illustrates change of inductance current in theprocess of controlling to switch from a PWM mode to a PFM mode using themode control device in FIG. 3;

FIG. 7 is a block diagram schematically illustrating a buck converterincluding the mode control device according to an embodiment of thepresent application; and

FIG. 8 is a flowchart schematically illustrating the mode control methodaccording to an embodiment of the present application.

DETAILED DESCRIPTION

The voltage converter to which the present application relates may be aboost converter, a buck converter, or a boost-buck converter etc. Thevoltage converter converts a supply voltage to voltages required byindividual electronic modules in an electronic apparatus, the electronicmodules for example are an RF amplifier, a display device, and so on.The electronic apparatus including electronic modules for example is amobile phone, a tablet computer, a monitor, an e-book reader, a portabledigital media player, and so on. Types of the voltage converter,electronics modules to which the power is supplied, and electronicapparatus to which it is applied does not constitute a limitation to thepresent application.

FIG. 1 is a block diagram schematically illustrating a voltage converterincluding the mode control device according to an embodiment of thepresent application. The voltage converter 100 shown in FIG. 1 convertsan input voltage Vin into an output voltage Vout, which may be used forpowering a load.

As shown in FIG. 1, the voltage converter 100 may comprise: a voltageconversion circuit 110 including a triode 101 and an inductor 103, theinductor 103 being located between an output terminal of the triode 101and a port of the output voltage Vout and for performing charging anddischarging operations, the triode 101 being for operating under drivingof the drive signal Sd to control the charging and dischargingoperations of the inductor 103; a feedback circuit 120 for receiving anoutput feedback (e.g., output voltage Vout) of the voltage converter100, comparing it with a reference voltage Vref that corresponds to atarget voltage to be output, and outputting an error control signal Se;a logic drive unit 130 for adjusting an operation mode for the voltageconversion circuit 110, generating a drive signal Sd for driving thetriode 101 according to the error control signal Se output by thefeedback circuit 120, so as to obtain the desired output voltage Vout;and a mode control device 140 for generating a mode switching signal Smthat controls switching from a continuous control mode to adiscontinuous control mode based on the inductance current on theinductor 103, the mode switching signal Sm enabling the voltageconverter to switch from the continuous control mode to thediscontinuous control mode at a constant load current threshold, theload current threshold being constant means that the load currentthreshold is independent of the input voltage Vin and the output voltageVout.

As shown in FIG. 1, in addition to the triode 101 and the inductor 103,the voltage conversion circuit 110 may further comprise: a diode 102having a cathode connected to the input voltage Vin via the triode 101,and having an anode being grounded; and a capacitor 104 connectedbetween the port of the output voltage Vout and the ground, for ensuringstable output of the output voltage Vout.

During the charging process, the triode 101 is turned on, the diode 102is open, the inductor 103 is charged and the inductance current isgenerated; since the input voltage Vin is direct current (DC), theinductance current on the inductor 103 increases linearly with a certainrate, correspondingly, current passes through two ends of the load, soas to have the output voltage. During the discharging process, thetriode 101 is tuned off, the diode 102 is in a short circuit, because ofa holding characteristic of the inductance current, the current thatpasses through the inductor L will slowly decrease from a value when thecharging is completed, until a next charging process starts or thecurrent value drops to zero, correspondingly, the inductor L starts tocharge the capacitor C, thereby the output voltage Vout is maintained.

The triode 101 in FIG. 1 is a control device for controlling thecharging and discharging operations of the voltage converter. In thevoltage conversion circuit 110 in FIG. 1, the diode 102 may also bereplaced with a triode, this alternative triode is turned off during thecharging process, and turned on during the discharging process. Thelogic drive unit 130 may generate a drive signal for the alternativetriode. In this case, the control device for controlling the voltageconverter includes both the triode 101 and this alternative triode.

The voltage converter 110 in FIG. 1 is a buck conversion circuit. In acase where the voltage converter is a boost converter, the voltageconversion circuit 110 is a boost conversion circuit; in a case wherethe voltage converter is a boost-buck converter, the voltage conversioncircuit 110 is a boost-buck conversion circuit. FIG. 2 schematicallyillustrates a circuit diagram of a boost conversion circuit in a boostconverter.

As shown in FIG. 2, the boost conversion circuit comprises: an inductor203 for receiving the input voltage Vin, and being grounded via thetriode 201, the inductor 203 being charged during the turn-on time Tonand discharged during the turn-off time Toff; a capacitor 204 having oneend connected to a connection point of the inductor 203 and the triode201 via the triode 202, and the other end being grounded, the capacitor204 being for ensuring stable output of the output voltage Vout. Thetriodes 201 and 202 may control the conversion operation of the voltageconversion circuit 110 under driving of the drive signal output from thelogic drive unit 130. During the charging process, the triode 201 isturned on, the triode 202 is turned off; in the discharging process, thetriode 201 is turned off, the triode 202 is turned on. The triodes 201and 202 are control devices in the boost converter. Similarly, there maybe more control devices for the boost-buck voltage conversion circuit ofthe boost-buck voltage converter.

The feedback circuit 120 forms a feedback loop for the voltage converter100, which, for example, may be implemented by an error amplifier,compares the output voltage Vout with the reference voltage Vref, andgenerates an error control signal Se, thereby controlling the chargingand discharging operations, so that the output voltage Vout is close toa desired target voltage. Furthermore, the feedback circuit 120 mayfurther includes a voltage divider for dividing the output voltage Vout,and use the error amplifier to compare a portion of the output voltageVout with the corresponding reference voltage.

The logic drive unit 130 may control the operation mode of the voltageconversion circuit 110 according to the mode switching signal Sm outputfrom the mode control device 140, the operation mode may, for example,include a continuous control mode, a discontinuous control mode etc. Thecontinuous control mode may for example be a pulse width modulation(PWM), and the discontinuous control mode may for example be a pulsefrequency modulation (PFM).

In the pulse width modulation mode, the voltage converter has a fixedon-off frequency fsw, which is equal to a reciprocal of a work periodTsw of the control device of the voltage converter, i.e.,fsw=1/Tsw=1/(Ton+Toff), wherein Ton is a turn-on time during which aswitch (e.g., triode 101 in FIG. 1) is turned on to charge and Toff is aturn-off time during which the switch is turned-off to discharge; duringthe operation process of the voltage converter, the charging anddischarging operations are changed by changing the turn-on time Ton andthe turn-off time Toff, but the turn-on time Ton cannot be infinitelysmall, for it is hard for the voltage converter to work in the pulsewidth modulation mode when the load driven by the voltage converter isvery small. Accordingly, the pulse width modulation mode is usuallyapplied to cases in which the load driven by the voltage converter is amedium or heavy load. In the pulse frequency modulation mode, the on-offfrequency fsw of the voltage converter may vary, and may be zero, i.e.,the voltage converter may be in a discontinuous control mode in which itoperates discontinuously, and thereby being applicable to a case wherethe load driven by the voltage converter is the light load.

As for when the load of the voltage converter is a medium load or alight load, it may be determined by setting a load threshold based on aninput voltage, a driving capability of the voltage converter etc., ifthe load of the voltage converter is greater than or equal to the loadthreshold, then it is a medium load, if the load of the voltageconverter is less than the load threshold, then it is a light load orheavy load. As an example, when the input voltage of the voltageconverter is relatively high, the load threshold becomes larger; whenthe input voltage of the voltage converter is relatively small, the loadthreshold becomes smaller.

The logic drive unit 130 also receives the error control signal Se fromthe feedback circuit 120, and generates a drive signal Sd for drivingthe triode 101 based on the mode switching signal Sm and the errorcontrol signal Se, so as to obtain the desired output voltage Vout. Asfor the logic drive unit including the respective operation modes, itmay be implemented with the existing techniques or a variety oftechniques that may appear in the future, and its specificimplementations do not constitute a limitation to the embodiments ofpresent technical.

Hereinafter, for convenience of the description, it is assumed that whenthe load of the voltage converter changes from a medium load to a lightload, the voltage converter switches from the pulse width modulation tothe pulse frequency modulation. This is merely an example, andembodiments of the present application can also be applied to switchingfrom other continuous control modes to other discontinuous controlmodes.

In the conventional mode control technique, whether to switch from thecontinuous control mode to the discontinuous control mode can bedetermined for example based on current (i.e., load current) on the loaddriven by the voltage converter, and the switching threshold in thismode control technique usually varies along with the input voltage Vinand the output voltage Vout of the voltage converter, which makes itdifficult to perform mode switching accurately. Thus, power efficiencyof the voltage converter decreases accordingly. Variation of the on-offfrequency in the control device will also increase noise in the outputvoltage Vout.

The mode control device 140 according to the embodiment of the presentapplication can generate a mode switching signal Sm for controlling thevoltage converter to switch from the continuous operation mode to thediscontinuous operation mode based on the inductance current I_(L) onthe inductor 103. The mode switching signal Sm is independent of theinput voltage Vin and the output voltage Vout of the voltage converter.In the voltage converter, according to a principle of conservation ofenergy, when the driven load reduces from a medium load to a light load,the current flowing through the load reduces accordingly, thus it needsto switch from a continuous control mode to a discontinuous control modeby, for example, switching from the pulse width modulation mode to thepulse frequency modulation mode. When the load current I_(Load) flowingthrough the driven load decreases, the inductance current I_(L) flowingthrough the inductor in the voltage conversion circuit of the voltageconverter (e.g., inductor 103 in FIG. 1, inductor 203 in FIG. 2) alsodecreases; when the load current I_(Load) flowing through the drivenload increases, the inductance current I_(L) flowing through theinductor also increases. Accordingly, in the present application, themode switching signal Sm for controlling the voltage converter to switchfrom a continuous operation mode to a discontinuous operation mode isgenerated based on the inductance current I_(L). The mode control device140 compares the inductance current I_(L) with the compensated switchingthreshold, determines whether to switch from a continuous operation modeto a discontinuous operation mode based on the comparison result, andgenerates the corresponding mode control signal Sm. The mode controlsignal Sm compensates for change of the input voltage Vin and the outputvoltage Vout in the voltage converter, so that the voltage converterswitches from a continuous operation mode to a discontinuous operationmode at a constant load current threshold, rather than changing the loadcurrent threshold according to the input voltage Vin and the outputvoltage Vout. The mode control device 140 will be described in furtherdetail below.

The voltage converter to which the mode control device is applied asdescribed in the embodiment of the present application is merelyillustrative, and may also include other sections. For example, it mayinclude a frequency oscillator, a low current control circuit forcontrolling a low current in the pulse frequency modulation mode, and soon.

FIG. 3 is a block diagram schematically illustrating the mode controldevice (140 in FIG. 1) according to an embodiment of the presentapplication. The mode control device may be applied to the voltageconverter described above in conjunction with FIGS. 1 and 2, and itincludes, but is not limited to, a boost converter, a buck converter, aboost-buck converter etc.

As shown in FIG. 3, the mode control device 140 may include: aninductance signal detection unit 141 for detecting inductance currentflowing on the inductor in the voltage conversion circuit 110, andoutputting a detection signal; a compensation unit 142 for compensatingfor change of the input voltage Vin and the output voltage Vout of thevoltage converter so as to switch from a continuous control mode to adiscontinuous control mode at a constant load current threshold, andoutputting a compensated switching threshold corresponding to theinductance current; and a mode switching determination unit 143 fordetermining whether to switch from a continuous control mode to adiscontinuous control mode based on the detection signal from theinductance signal detection unit 141 and the switching threshold fromthe compensation unit 142, and generating a mode control signal Smindicating whether to switch from the continuous control mode to thediscontinuous control mode.

The detection signal output by the inductance signal detection unit 141may be inductance current flowing on the inductor in the voltageconversion circuit 110, or may also be a voltage signal corresponding tothe inductance current. The inductance signal detection unit 141 mayadopt various techniques to detect the inductance current flowing on theinductor (e.g., inductor 103 in FIG. 1 and inductor 203 in FIG. 2). Forexample, it may use a resistor with an extremely small resistance toseparate a small part of current signals from the inductor, or it mayalso use a variable resistance area of a power tube (e.g., MOSFET) todetect the inductance current, and accordingly, the inductance signalmay be detected by detecting a voltage between a source and a drain whenit operates in the variable resistance area. The techniques fordetecting the inductance signal as adopted by the inductance signaldetection unit 141 do not constitute a limitation to the embodiments ofthe present application.

The compensation unit 142 can compensate for change of the input voltageVin and the output voltage Vout of the voltage converter, so that thevoltage converter switches from the continuous control mode to thediscontinuous control mode at a constant load current threshold.Hereinafter, description is provided with the voltage converter being abuck converter (e.g., having a buck converter unit 110 shown in FIG. 1),and where the continuous control mode is the PWM control mode, and thediscontinuous control mode is the PFM control mode as an example.

FIG. 4 schematically illustrates a signal diagram of inductance currentof a buck converter in a PWM mode. As shown in FIG. 4, the inductor ischarged during a time period of Ton, the inductance current I_(L)increases accordingly, until it increases to a maximum I_(Lmax); theinductor is discharged during a time period of Toff, the inductancecurrent decreases from the maximum I_(Lmax) accordingly, until it isreduced to a minimum I_(Lmin). And so on, and so forth. Differencebetween the maximum and the minimum of the inductance current I_(L)represents a current ripple ΔI_(L) on the inductor, and the followingEquation (1) representing the current ripple ΔI_(L) can be obtainedaccording to the inductance current of the voltage converter during theturn-on time Ton and turn-off time Toff:

$\begin{matrix}{{\Delta \; I_{L}} = \frac{{Tsw}*\left( {{Vin} - {Vout}} \right)*{Vout}}{L*{Vin}}} & {{Equation}\mspace{14mu} (1)}\end{matrix}$

where Tsw is a work cycle of the buck converter, and equal to a sum ofthe turn-on time Ton and turn-off time Toff, Vin is the input voltage ofthe buck converter, Vout is the output voltage of the buck converter,and L is the inductance value of the inductor (103 in FIG. 1) in thebuck converter.

In FIG. 4, taking value of the inductance current being zero as aboundary, curve of the inductance current above the value of zero form apositive triangle, curve of the inductance current below the value ofzero form an negative triangle, value of the positive triangular andthat of the negative triangular are calculated respectively and thenadded, to obtain a relationship among the current I_(Load) on the loaddriven by the buck converter, the current ripple ΔI_(L), and the minimumI_(Lmin) of the inductance current, as shown in the following Equation(2):

$\begin{matrix}{I_{Load} = {\frac{\left( {{\Delta \; I_{L}} - {\Delta \; I_{L\mspace{11mu} \min}}} \right)^{2} - {\Delta \; I_{L\mspace{11mu} \min}^{\; 2}}}{2*\Delta \; I_{L}}.}} & {{Equation}\mspace{14mu} (2)}\end{matrix}$

The Equation (2) can be simplified to the following Equation (3):

$\begin{matrix}{I_{Load} = {\frac{\Delta \; I_{L}}{2}\; - {I_{L\mspace{11mu} \min}.}}} & {{Equation}\mspace{14mu} (3)}\end{matrix}$

As described in the preceding, when the load current I_(Load) flowingthrough the driven load decreases, the inductance current I_(L) flowingthrough the inductor of the voltage converter also decreases. When theload current I_(Load) is a minimum in the PWM mode (i.e.,I_(Load)=I_(PFM)), the voltage converter switches to the PFM mode,accordingly, the inductance current I_(L) on the inductor also reachesits minimum, i.e., reaching a switching threshold I_(LZC) based on whichmode switching is to be carried out. Accordingly, Equation (3) can betransformed into the following Equation (4):

$\begin{matrix}{I_{LZC} = {\frac{\Delta \; I_{L}}{2}\; - {I_{PFM}.}}} & {{Equation}\mspace{14mu} (4)}\end{matrix}$

The following Equation (5) can be obtained by substituting Equation (1)into Equation (4):

$\begin{matrix}{{\Delta \; I_{LZC}} = {\frac{{Tsw}*\left( {{Vin} - {Vout}} \right)*{Vout}}{2*L*{Vin}} - {I_{PFM}.}}} & {{Equation}\mspace{14mu} (5)}\end{matrix}$

According to Equation (5), it can be known that, when the mode controldevice 140 according to the embodiment of the present applicationdetermines to switch from a continuous operation mode to a discontinuousoperation mode based on the switching threshold I_(LZC) of theinductance current I_(L), Equation (5) may be achieved by thecompensation unit 142. During the process where the compensation unit142 achieves Equation (5), it may keep I_(PFM) constant by compensatingfor change of the input voltage Vin and the output voltage Vout whenachieving the first item in Equation (5).

For the PWM mode, both Tsw and L at the right side of Equation (5) arefixed, I_(PFM) is fixed also and may be preset, thus the compensationunit 142 can detect the input voltage Vin and the output voltage Vout ofthe voltage converter, and then achieve Equation (5). The compensationunit 142 may compensate for change of the input voltage Vin and theoutput voltage Vout of the voltage converter, so as to ensure switchingfrom the PWM mode to the PFM mode at a constant load current I_(PFM).

Alternatively, in order to more conveniently achieve the compensationunit 142, Equation (5) may also be transformed to the following Equation(6):

$\begin{matrix}{{I_{LZC} = {\frac{{Tsw}*\left( {1 - D} \right)*{Vout}}{2*L} - I_{PFM}}},} & {{Equation}\mspace{14mu} (6)}\end{matrix}$

where D is a duty cycle of the voltage converter and equals to Vout/Vin.The (1−D)*Vout in Equation (6) may be achieved by sampling Vout, wherethe sampling clock is fsw, because fsw is composed by the turn-on timeTon and turn-off time Toff, and the (1−D) is equal to Toff*fsw.Therefore, (1−D)*Vout in Equation (6) can be implemented conveniently.Tsw and L in Equation (6) are given when designing the voltageconverter, and the load current I_(PFM) is also a constant value, thusEquation (6) can be achieved conveniently to obtain the switchingthreshold I_(LZC).

The above description provided in conjunction with Equations (1) to (6)shows an example of how to set the switching threshold I_(LZC) in thebuck converter so as to maintain I_(PFM) constant. When the voltageconverter changes, setting of the switching threshold I_(LZC) is alsoprobable to change appropriately. For example, when the voltageconverter is a boost converter, Equation (1) used above for the currentripple ΔI_(L) of the buck converter is changed to the following Equation(7):

$\begin{matrix}{{{\Delta \; I_{L}} = \frac{{Tsw}*\left( {1 - D} \right)*\left( {{Vout} - {Vin}} \right)}{L}},} & {{Equation}\mspace{14mu} (7)}\end{matrix}$

where D is a duty cycle of the boost converter, and equals to(Vout-Vin)/Vout, but not equals to Vout/Vin of the buck converter.Further, the above Equation (4) becomes the following Equation (8):

$\begin{matrix}{I_{Load} = {{\frac{\Delta \; I_{L}}{2}\left( {1 - D} \right)} - {\Delta \; {I_{L\mspace{11mu} \min}.}}}} & {{Equation}\mspace{14mu} (8)}\end{matrix}$

The following Equation (9) can be obtained by replacing Equation (7)into Equation (8):

$\begin{matrix}{I_{LZC} = {\frac{{Tsw}*\left( {1 - D} \right)^{2}*\left( {{Vout} - {Vin}} \right)}{2*L} - {I_{PFM}.}}} & {{Equation}\mspace{14mu} (9)}\end{matrix}$

FIG. 5 is a circuit diagram schematically illustrating that thecompensation unit 142 obtains the switching threshold I_(LZC) fromEquation (6). As shown in FIG. 5, for convenience of the description,the circuit diagram of the compensation unit 142 is divided into fiveblocks, Block 1 to Block 5, as shown by each block in FIG. 5. In block1, an on-off control signal with a frequency of fsw is used tosample/hold the output voltage Vout of the voltage converter; then, lowpass filtering is performed on the sampled Vout signal using Block 2, soas to obtain the (1−D)*Vout in Equation (6) (i.e., the output DC level);in Block 3, a voltage signal output from Block 2 is converted into acurrent signal, Tsw/2L is determined, and multiplied with a currentsignal corresponding to (1−D)*Vout, so as to obtain the first item inEquation (6); in Block 4, a preset constant load current I_(PFM) isobtained using a current source, and the load current I_(PFM) issubtracted from the first item in Equation (6); Equation (6) is alreadyachieved using Blocks 1 to 4, but what is output from Block 4 is acurrent signal, in Block 5, the current signal output from Block 4 isconverted into a voltage signal for subsequent processing.

The mode switching determination unit 143 determines whether to switchfrom a continuous control mode to a discontinuous control mode based onthe detection signal from the inductance signal detection unit 141 andthe switching threshold from the compensation unit 142. When thedetection signal from the inductance signal detection unit 141 isgreater than the switching threshold I_(LZC) from the compensation unit142, the mode determination unit 143 determines not to switch from thecurrent PWM mode (e.g., the continuous control mode) into the PFM mode(e.g., the discontinuous control mode); when the detection signal fromthe inductance signal detection unit 141 is equal to or smaller than theswitching threshold I_(LZC) from the compensation unit 142, the modedetermination unit 143 determines to switch from the current PWM modeinto the PFM mode. After determining whether to switch from a continuouscontrol mode to a discontinuous control mode, the mode switchingdetermination unit 143 generates a mode control signal Sm indicatingwhether to switch from the continuous control mode to the discontinuouscontrol mode.

When the inductance signal from the inductance signal detection unit 141is a current signal, the switching threshold I_(LZC) can be obtainedfrom the above Equation (5), the mode switching determination unit 143may be implemented by a current comparator to perform comparison. Whenthe inductance signal from the inductance signal detection unit 141 is avoltage signal, accordingly, the switching threshold I_(LZC) may beconverted into a voltage, and the mode switching determination unit 143may be implemented by a voltage comparator to perform comparison. Thecomparator (PFM comp) in FIG. 5 is a specific implementation of the modeswitching determination unit 143, and it compares the voltage signalgenerated by the compensation unit 142 based on Equation (6) with avoltage Vsen on the inductor detected by the inductance signal detectionunit 141, so as to generate the mode control signal Sm indicatingwhether to switch from the continuous control mode to the discontinuouscontrol mode.

FIG. 6 schematically illustrates change of inductance current in theprocess of controlling to switch from the PWM mode to the PFM mode bythe mode control device 140 in FIG. 3. As shown in FIG. 6, the voltageconverter operates in the PWM mode initially, when the load driven bythe voltage converter gradually decreases, the inductance current I_(L)on the inductor gradually decreases. When the inductance current I_(L)on the inductor reaches the switching threshold I_(LZC) output by thecompensation unit 142, the mode control signal Sm output from the modeswitching determination unit 143 indicates switching from the PWM modeto the PFM mode, then the voltage converter switches from the PWM modeto the PFM mode. In the PFM mode, the voltage converter performscharging and discharging operations discontinuously, and limits theinductance current I_(L) on the inductor to be greater than zero.Herein, the inductance current I_(L) being limited to be greater thanzero is for improving operation efficiency in the PFM mode.

In the mode control device according to the embodiment of the presentapplication, whether to switch from the continuous control mode to thediscontinuous control mode is determined based on the inductance currentflowing on the inductor in the voltage conversion circuit 110, and thechange of the input voltage and the output voltage is compensated whendetermining the switching threshold, so that the voltage converter canswitch from the continuous control mode to the discontinuous controlmode accurately at a constant load current threshold, which improvespower efficiency of the voltage converter and reduces noise in theoutput voltage Vout caused by change of the on-off frequency.

FIG. 7 is a block diagram schematically illustrating a buck converterincluding the mode control device according to an embodiment of thepresent application. The voltage conversion circuit 110, feedbackcircuit 120, logic drive unit 130, and mode control device 140 in FIG. 7are the same as those in FIG. 1, and adopt the same reference numerals.FIG. 7 differs from FIG. 1 in that a zero-crossing comparator 150 isadded, the zero-crossing comparator 150 starts a comparison operationwhen the voltage converter enables the PFM mode, for determining whetherthe inductance current on the inductor changes from a positive currentto zero, and outputting a zero-crossing indication signal indicatingwhether the inductance current is larger than zero. When thezero-crossing comparator 150 determines that the inductance currentchanges from the positive current to zero, it instructs the logic driveunit 130 to stop the discharging operation of the voltage converter, inorder to ensure that the inductance current of the voltage converter isgreater than zero when the voltage converter is in the PFM mode (asshown in FIG. 5).

As shown in FIG. 7, one input of the zero-crossing comparator 150 isgrounded, another input thereof is connected to the inductance currentoutput by the inductance signal detection unit 141, and starts or stopsa comparison operation under control of the mode switching determinationunit 143. When the mode control signal Sm output by the mode switchingdetermination unit 143 indicates to switch from the PWM mode to the PFMmode, the zero-crossing comparator 150 is enabled to start comparing theinductance current on the inductor with zero, and generates thezero-crossing indication signal indicating whether the inductancecurrent on the inductor is greater than zero. When the zero-crossingindication signal of the zero-crossing comparator 150 indicates that theinductance current on the inductor is equal to or less than zero, thelogic drive unit 130 may drive a switch of the voltage convertingcircuit to make the current on the inductor be greater than zero.

In the voltage converter described in conjunction with FIG. 7, whetherto switch from the PWM mode to the PFM mode is determined based on theinductance current flowing on the inductor in the voltage conversioncircuit 110, and change of the input voltage Vin and the output voltageVout is compensated when determining the switching threshold, so thatthe voltage converter can switch from the continuous control mode to thediscontinuous control mode accurately at a constant load currentthreshold, which improves power efficiency of the voltage converter andreduces noise in the output voltage caused by change of the on-offfrequency.

FIG. 8 is a flowchart schematically illustrating a mode control method800 according to an embodiment of the present application. The modecontrol method 800 is applicable for controlling the voltage converterswitches from a continuous operation mode to a discontinuous operationmode. The voltage converter converts an input voltage into an outputvoltage, which may be used for powering a load. The voltage convertermay be a boost converter, a buck converter, a boost-buck converter, andmay be for example the voltage converter described in conjunction withFIGS. 1 and 2. In particular, the voltage converter may include: avoltage conversion circuit including a control device and an inductor,the inductor being capable of performing charging and dischargingoperations, the control device being for operating under driving of adrive signal to control the charging and discharging operations of theinductor; and a logic drive unit for adjusting an operation mode for thevoltage conversion circuit, and generating the drive signal for drivingthe control device, so as to obtain a desired output voltage.

As shown in FIG. 8, the mode control method 800 may include: detectinginductance current flowing on an inductor for performing charging anddischarging operations in a voltage converter, and outputting adetection signal (S810); compensating for change of an input voltage andan output voltage of the voltage converter so as to switch from thecontinuous control mode to the discontinuous control mode at a constantload current threshold, and outputting a compensated switching thresholdcorresponding to the inductance current (S820); and determining whetherto switch from the continuous control mode to the discontinuous controlmode based on the detection signal and the switching threshold, andgenerating a mode control signal indicating whether to switch from thecontinuous control mode to the discontinuous control mode (S830).

In the conventional mode control technique, whether to switch from thecontinuous control mode to the discontinuous control mode is determinedusually based on the current (i.e., load current) on the load driven bythe voltage converter, and the switching threshold in this mode controltechnique usually varies along with the input voltage and the outputvoltage of the voltage converter, which makes it difficult to performmode switching accurately, and thus lowers power efficiency of thevoltage converter accordingly. Further, variation of the on-offfrequency in the control device will also increase noise in the outputvoltage.

The mode control method 800 according to the embodiment of the presentapplication can generate a mode switching signal for controlling thevoltage converter to switch from the continuous operation mode to thediscontinuous operation mode based on the inductance current on theinductor in the voltage converter, and the mode switching signal isindependent of the input voltage and the output voltage of the voltageconverter. This is based on the following facts: when the load currentflowing through the driven load decreases, the inductance currentflowing through the inductor in the voltage conversion circuit of thevoltage converter also decreases; when the load current flowing throughthe driven load increases, the inductance current flowing through theinductor also increases. Therefore, it is possible to control to switchfrom the continuous control mode to the discontinuous control mode basedon the inductance current on the inductor in the voltage converter,instead of the load current.

The detection signal output in S810 may be inductance current flowing onthe inductor in the voltage conversion circuit, and may also be avoltage signal corresponding to the inductance current. Varioustechniques may be adopted to detect the inductance current flowing onthe inductor, for example, a resistor with an extremely small resistancemay be used to separate a small part of current signals from theinductor, or a variable resistance area of a power tube may be used todetect the inductance current, and accordingly the inductance signal maybe detected by detecting a voltage between a source and a drain of thepower tube when it operates in the variable resistance area. Thetechniques for detecting the inductance signal as adopted in S810 do notconstitute a limitation to the embodiments of the present application.

In S820, a switching threshold corresponding to the inductance currentis generated by compensating change of the input voltage and the outputvoltage of the voltage converter, so that the voltage converter switchesfrom the continuous control mode to the discontinuous control mode at aconstant load current threshold.

In the case where the voltage converter is a buck converter, thecontinuous control mode is the PWM control mode, and the discontinuouscontrol mode is the PFM control mode. As described in conjunction withFIG. 4, the switching threshold corresponding to the inductance currenton the inductor can be generated based on Equation (5). From Equation(5) it can be seen that, in an implementation, threshold of the loadcurrent may be maintained constant, but change of the input voltage Vinand the output voltage Vout is compensated when achieving the first itemin Equation (5). The load current threshold being constant means thatthreshold of the load current is independent of the input voltage andthe output voltage, so that it is possible to switch from the continuouscontrol mode to the discontinuous control mode accurately. In Equation(5), both Tsw and L are fixed, I_(PFM) is fixed and may be preset, andwhen the operation of S820 is implemented, input and output voltages ofthe voltage converter may be obtained, thereafter Equation (5) isachieved.

Alternatively, in order to more conveniently implement the operation ofS820, it is also possible to change Equation (5) into theabove-described Equation (6), achieve the (1−D)*Vout Equation (6) bysampling Vout at a sampling clock fsw, i.e., Toff * fsw * Vout, thusconveniently achieving the (1−D)*Vout in Equation (6), and Tsw and L inEquation (6) are given when designing the voltage converter, and theload current I_(PFM) is also a constant value, thus Equation (6) can beachieved conveniently to obtain the switching threshold I_(LZC). As forthe specific implementations of obtaining the switching thresholdI_(LZC) based on Equation (6) in S820, descriptions provided inconjunction with FIG. 5 can be referred to.

In the case where the voltage converter is a boost converter, thecontinuous control mode is the PWM control mode, and the discontinuouscontrol mode is the PFM mode, the switching threshold I_(LZC) can beobtained based on Equation (9) in S820 so as to maintain I_(PFM)constant.

In S830, whether to switch from the continuous control mode to thediscontinuous control mode is determined based on the detection signalobtained in S810 and the switching threshold obtained in S820. When thedetection signal obtained in S810 is greater than the switchingthreshold obtained in S820, it is determined not to switch from thecontinuous control mode (e.g., the PWM mode) into the discontinuouscontrol mode (e.g., the PFM mode); when the detection signal obtained inS810 is equal to or smaller than the switching threshold obtained inS820, it is determined to switch from the continuous control mode intothe discontinuous control mode. After whether to switch from thecontinuous control mode to the discontinuous control mode is determined,a mode control signal Sm indicating whether to switch from thecontinuous control mode to the discontinuous control mode is generated.

When the detection signal obtained in S810 is a current signal, in S820,the switching threshold I_(LZC) being a current signal can be obtainedfrom the above Equations (5), (6) or (9) in S820, and a currentcomparator is used to perform comparison so as to generate the modecontrol signal Sm in S830. When the detection signal obtained in S810 isa voltage signal, the switching threshold can be converted into avoltage accordingly in S820, and a voltage comparator is used to performcomparison so as to generate the mode control signal Sm in S830.

In the mode control method according to the embodiment of the presentapplication, whether to switch from the continuous control mode to thediscontinuous control mode is determined based on the inductance currentflowing on the inductor in the voltage converter, and change of theinput voltage and the output voltage of the voltage converter iscompensated when determining the switching threshold, so that thevoltage converter can switch from a continuous control mode to adiscontinuous control mode accurately at a constant load currentthreshold, which improves power efficiency of the voltage converter andreduces noise in the output voltage caused by change of the on-offfrequency.

It is noted that the PWM mode and PFM mode in the above text are merelyexamples of the continuous control mode and the discontinuous controlmode respectively. In practice, it is also possible to carry outswitching from other continuous control modes besides the PWM mode toother discontinuous control modes besides the PFM mode.

In the various examples described herein, references are made totriodes. It will be understood that such triodes can include transistorssuch as field-effect transistors (FETs). Such FETs can include, forexample, MOSFET devices and/or transistors implemented in other processtechnologies. Other types of transistors can be utilized to implementone or more features of the present disclosure.

Those skilled in the art can understand, for convenience and simplicityof the description, the specific implementations of the methodembodiments described above can be referred to corresponding process inthe preceding product embodiments.

Those with ordinary skill in the art can appreciate that, devices andalgorithm steps described with reference to the embodiments disclosed inthis application may be implemented through electronic hardware, or acombination of the electronic hardware and software. As for eachspecific application, a person skilled in the art can use differentmethods to implement the described functions, but such implementationsshould not be construed as being beyond the scope of the presentinvention.

Principles and advantages of technical solutions described above areapplicable to any voltage converter. The voltage converter can beapplied in a variety of electronic apparatuses, which may include, butnot are limited to, an electronic product, a portion of an electronicproduct, an electronic test equipment etc. The consumer electronicproduct may include, but is not limited to, a smart phone, a TV, atablet computer, a monitor, a personal digital assistant, a camera, anaudio player, a memory etc. A portion of the consumer electronic productmay include a multi-chip module, a power amplifier module etc.

The above described are only specific implementations of the presenttechnical solution, but the scope of the present technical solution isnot limited thereto, and any alternatives and equivalents that can beconceivable by a person skilled in the art should be encompassed withinthe scope of protection of the present technical solution.

What is claimed is:
 1. A voltage converter comprising: a voltageconversion circuit including an inductor configured to be charged anddischarged to facilitate conversion of an input voltage to an outputvoltage, the voltage conversion circuit further including a switchconfigured to allow the inductor to be charged and discharged; a logicdrive unit configured to provide a drive signal to the switch to controlthe charging and discharging of the inductor; and a mode control unitconfigured to provide a mode-switching signal to the logic drive unit tocontrol switching between a continuous control mode and a discontinuouscontrol mode based on an inductance current associated with the inductorand a load-current threshold.